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Publication numberUS7835595 B2
Publication typeGrant
Application numberUS 11/652,534
Publication dateNov 16, 2010
Filing dateJan 12, 2007
Priority dateAug 23, 2006
Fee statusPaid
Also published asUS20080050044
Publication number11652534, 652534, US 7835595 B2, US 7835595B2, US-B2-7835595, US7835595 B2, US7835595B2
InventorsHui-Fen Chia, Ying-Yuan Tang
Original AssigneePrincton Technology Corporation
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Image processing system and method for image scaling
US 7835595 B2
Abstract
An image processing method for scaling an image from an original resolution to a target resolution is provided. A pixel value PT of a target pixel point NT in the target resolution is theoretically composed of original pixel values P1-PK of original pixel points N1-NK in the original resolution, wherein K is a positive integer larger than 1. First, theoretical combination ratios R1-RK corresponding to the original pixel points N1-NK are found. Then, the theoretical combination ratios R1-RK are converted to corresponding weights W1-WK, wherein each of the corresponding weights W1-WK is an integer between 1 and 2n, n is an integer, and the sum of the corresponding weights W1-WK is 2n. The original pixel values P1-PK are calculated with the corresponding weights W1-WK using a scaler, to generate the pixel value PT of the target pixel point NT and complete the image processing.
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Claims(14)
1. An image processing method for scaling an image from an original resolution to a target resolution, wherein a pixel value PT of a target pixel point NT in the target resolution is theoretically composed of original pixel values P1-PK of original pixel points N1-NK in the original resolution, and K is a positive integer larger than 1, the method comprising:
a computer performing the steps of:
finding theoretical combination ratios R1-RK corresponding to the original pixel points N1-NK;
converting the theoretical combination ratios R1-RK to corresponding weights W1-WK, wherein each of the corresponding weights W1-WK is an integer between 1 and 2n, n is an integer, and the sum of the corresponding weights W1-WK is 2n; and
calculating the original pixel values P1-PK with the corresponding weights W1-WK using a scaler, to generate the pixel value PT of the target pixel point NT and complete the image processing,
wherein converting the theoretical combination ratios R1-RK to corresponding weights W1-WK further comprise checking a look-up table to obtain the corresponding weights W1-WK, wherein the look-up table has a plurality of table fields, each having a field order, and provides a conversion rule from a value to an integer not larger than 2n, and n is an integer, and
wherein checking the look-up table to obtain the corresponding weights W1-WK further comprise:
providing a theoretical combination ratio RK;
determining whether the theoretical combination ration RK being look up is less than a limit value; and
setting the corresponding weight WK to zero if the theoretical combination ratio RK being looked up is less than the limit value.
2. The method as claimed in claim 1, wherein converting the theoretical combination ratios R1-RK to corresponding weights W1-WK further comprises obtaining the corresponding weight WK by:
W K = 2 n - i = 1 K - 1 W i .
3. The method as claimed in claim 1, wherein a corresponding weight WK is equal to the field order of a table field of the look-up table if a reference value within the table field of the look-up table exceeds or equals the theoretical combination ratio Rk, in which 1≦k≦K.
4. The method as claimed in claim 1, wherein the corresponding the corresponding weight Wk is determined to be the field order of a first table field of the look-up table or the field order of a second table field of the look-up table using a half-adjust rounding or a rounding off method when a theoretical combination ratio Rk is between a first reference value within the first table field and a second reference value within the second table field, in which 1≦k≦K.
5. The method as claimed in claim 1, wherein the look-up table comprises a plurality of reference values and the reference values are associated with the original resolution.
6. The method as claimed in claim 1, wherein calculating the original pixel values P1-PK with the corresponding weights W1-WK using a scaler to generate the pixel value PT of the target pixel point NT further comprises:
generating the pixel value PT of the target pixel point NT by:
P T = i = 1 K P i W i 2 n .
7. A system for scaling an image from an original resolution to a target resolution, wherein a pixel value PT of a target pixel point NT in the target resolution is theoretically composed of original pixel values P1-PK of original pixel points N1-NK in the original resolution, and K is a positive integer larger than 1, the method comprising:
a microcontroller for generating a look-up table according to the original resolution, wherein the look-up table has a plurality of table fields, each having a field order, and provides a conversion rule from a value to an integer not larger than 2n, and n is an integer;
a memory for providing the original pixel values P1-PK;
a table index generator for obtaining from the look-up table corresponding weights W1-WK according to theoretical combination ratios R1-RK corresponding to the original pixel points N1-NK, wherein each of the corresponding weights W1-WK is an integer between 1 and 2n, and sum of the corresponding weights W1-WK is 2n; and
a scaler for generating the pixel value PT of the target pixel point NT according to the original pixel values P1-PK and the corresponding weights W1-WK;
wherein the microcontroller find the theoretical combination ratios R1-RK and the table index generator further determines whether the theoretical combination ratio RK being look up is less than a limit value and sets the corresponding weight WK to zero if the theoretical combination ratio RK being looked up is less than the limit value.
8. The system as claimed in claim 7, wherein the scaler further comprises at least one n bit multiplier for performing the operating to generate the pixel value PT of the target pixel point NT.
9. The system as claimed in claim 7, wherein the table index generator obtains the corresponding weight WK by the formula:
W K = 2 n - i = 1 K - 1 W i .
10. The system as claimed in claim 7, wherein a corresponding weight WK is equal to the field order of a table field of the look-up table if a reference value within the table field of the look-up table exceeds or equals the theoretical combination ratio Rk, in which 1≦k≦K.
11. The method as claimed in claim 7, wherein the corresponding the corresponding weight Wk is determined to be the field order of a first table field of the look-up table or the field order of a second table field of the look-up table using a half-adjust rounding or a rounding off method when a theoretical combination ratio Rk is between a first reference value within the first table field and a second reference value within the second table field, in which 1≦k≦K.
12. The system as claimed in claim 7, wherein the look-up table comprises a plurality of reference values and the reference values are associated with the original resolution.
13. The system as claimed in claim 7, wherein the scaler generates the pixel value PT of the target pixel point NT using the formula:
P T = i = 1 K P i W i 2 n .
14. The system as claimed in claim 7, wherein the microcontroller further generates a second look-up table if the original pixel points N1-NK are two-dimensional pixel points.
Description
BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to image processing, and in particular, to an image processing system and method for scaling or resolution of an image.

2. Description of the Related Art

Image and display systems often require image resolution to be scaled up or down to meet various requirements. Images (pixels) resolution may be scaled upward from low resolution to high resolution. Images may also be scaled down when the original resolution is higher than the desired display resolution. When an original image is displayed in a different resolution to form a new image, the changed resolution causes the pixel value of each pixel point in a newly formed image to be formed by more pixel values of original pixel points in the original image with specific theoretical combination ratios applied thereto.

For example, if a pixel value of pixel point NA′ in the new image is formed by two pixel values of original pixel points NA and NB respectively in the original image, the pixel value of pixel point NA′ may be theoretically the summation of ⅔ the pixel value for pixel point NA and ⅓ the pixel value for pixel point NB or of half the pixel value summation of both pixel points NA and NB.

A common technique used to scale image resolution is linear interpolation. The linear interpolation utilizes pixel value of each pixel point needed for the new pixel point and its related theoretical combination ratio to generate the new pixel value of a pixel point in the new image resolution. As shown in FIG. 1, for example, if an image resolution is to be downscaled from an original resolution with 500 points to a target resolution with 300 points by 1D (one dimension) interpolation, new pixel values PA′, PB′ and PC′ of pixel points NA′, NB′ and NC′ respectively in the target resolution can be determined according to pixel values PA, PB, PC, PD and PE of pixel points NA, NB, NC, ND and NE respectively in the original resolution using following formulae:

P A = 300 P A + 200 P B 500 , ( 1 ) P B = 100 P B + 300 P C + 100 P D 500 , ( 2 ) P C = 200 P D + 300 P E 500 , ( 3 )
where the numbers 300 and 200 in formula (1) indicate theoretical combination ratios RA and RB for pixel values PA and PB forming the pixel value PA′, respectively. In addition, it can be observed from formula (1) to (3) that each theoretical combination ratio for the pixel value of pixel point NA, NB, NC, ND, or NE depends on the resolution used. In this example, each theoretical combination ratio is not exceeding 300 (i.e. the target resolution) and each denominator in the formula is 500 (i.e. the original resolution).

Scaling an image up or down directly by linear interpolation requires several multiplication and division operations, thus requiring hardware design with sufficient bit number of multipliers and dividers to perform the necessary operations. Typically, as the bit number of multiplier or divider increases, hardware cost and complexity increase accordingly. In this example, if the image is scaled from a resolution with 500 points to another resolution with 300 points, at least nine bits of multiplier/divider in the hardware are required to complete the operations.

Once the image is enlarged or becomes a two- or more dimension image, the bit number of multiplier/divider needed for hardware is also increased relatively. Accordingly, hardware costs and the time for operation increase.

Thus, a method and system for scaling image resolution with reduced hardware cost and operating time are desired.

BRIEF SUMMARY OF THE INVENTION

An exemplary embodiment of a system for scaling an image from an original resolution to a target resolution is provided, wherein a pixel value PT of a target pixel point NT in the target resolution is theoretically composed of original pixel values P1-PK of original pixel points N1-NK in the original resolution, and K is a positive integer larger than 1. The system comprises a microcontroller, a memory, a table index generator and a scaler. The microcontroller generates a look-up table according to the original resolution, wherein the look-up table provides a conversion rule from a value to an integer not larger than 2n, and n is an integer. The memory provides the original pixel values P1-PK. The table index generator obtains from the look-up table corresponding weights W1-WK according to theoretical combination ratios R1-RK corresponding to the original pixel points N1-NK, wherein each of the corresponding weights W1-WK is an integer between 1 and 2n. The scaler generates the pixel value PT of the target pixel point NT according to the original pixel values P1-PK and the corresponding weights W1-WK. The microcontroller generates the theoretical combination ratios R1-RK.

The invention also provides an image processing method for scaling an image from an original resolution to a target resolution, wherein a pixel value PT of a target pixel point NT in the target resolution is theoretically composed of original pixel values P1-PK Of original pixel points N1-NK in the original resolution, and K is a positive integer larger than 1. First, theoretical combination ratios R1-RK corresponding to the original pixel points N1-NK are found. Then, the theoretical combination ratios R1-RK are converted to corresponding weights W1-WK, wherein each of the corresponding weights W1-WK is an integer between 1 and 2n, n is an integer, and the sum of the corresponding weights W1-WK is 2n. The original pixel values P1-PK are calculated with the corresponding weights W1-WK by using the scaler to generate the pixel value PT of the target pixel point NT and complete the image processing.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequent detailed description and examples with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a conventional method for down-scaling image resolution;

FIG. 2 shows an embodiment of a scaling system according to the invention;

FIG. 3 shows an embodiment of a look-up table T according to the invention;

FIG. 4 is a flowchart of an image processing method according to an embodiment of the invention;

FIG. 5 shows a an image scaling method applied in a one dimensional (1D) image according to an embodiment of the invention;

FIG. 6A shows a conventional image scaling method applied in a two dimensional (2D) image;

FIG. 6B shows an image scaling method applied in a two dimensional image according to an embodiment of the invention;

FIG. 7A shows another embodiment of a look-up table T for up-scaling an image according to the invention;

FIG. 7B shows a conventional image up-scaling method applied in a two dimensional image; and

FIG. 7C shows an image up-scaling method applied in a two dimensional image according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.

The invention provides a method and system to convert the theoretical combination ratios R1-RK corresponding to original pixel points N1-NK originally used by linear interpolation to smaller values using a digital processor or a microcontroller such that the aforementioned operations can be completed by a smaller bit number of multiplier/dividers. According to the invention, if the bit number of multiplier is an integer n, the combination ratios will be changed from a value, such as several hundreds, to a small integer between 1 and 2n by checking a table, such that the factors of the multiplication/division operations performed to the combination ratios are reduced from a large range to a small range. Reduced bit number of multipliers and no requirement for a divider reduce hardware cost and simplify related operations.

FIG. 2 shows an embodiment of a scaling system according to the invention. Scaling system 200 comprises a microcontroller 210, a memory 220, a table index generator 230 and a scaler 240. The memory 220 stores original pixel values P1-PK of all original pixel points N1-NK in original resolution and may send the pixel values P1-PK to the scaler 240 for further operation, wherein K is an integer larger than 1. A look-up table T generated by the microcontroller 210 is stored in a storage device (not shown).

The look-up table T provides a conversion rule from a reference value to an integer not larger than 2n. To do this, for example, the look-up table T is divided into several table fields, in which a table field CX represents the Xth table field on the table T, and X represents its related field order. For example, the table field C1 represents the 1st table field on the table T and its related field order is set to one, the table field C2 represents the 2nd table field on the table T and its related field order is set to two and so on. In other words, the value of a specific field order X can be derived from the table field CX on the table T. In addition, each table field CX on the table T has a reference value UX, and bigger field order X gets bigger reference value. For example, if the table fields C1 and C2 have reference values U1 and U2 respectively, the reference value U2 should be bigger than the reference value U1 due to the related field order of table field C2 is bigger than that of table field C1. The range for the field order X of the table field CX depends on bit number n of multiplier utilized while the range for the reference value UX depends on original resolution.

The table index generator 230 generates table indices based on table T for looking up and finding a table field on table T according to a specific theoretical combination ratio RK. The table index generator 230 also stores memory addresses of the pixel values P1-PK so as to obtain a specific pixel value PK from the memory 220. The related field order of the found table field is set to a corresponding weight WK corresponding to the specific theoretical combination ratio RK. The scaler 240 comprises at least one n bit number of multiplier (not shown), performing the multiplication operations to generate the pixel value PT of the target pixel point NT in new resolution (target resolution) after scaling. The scaler 240 generates new pixel value PT of the target pixel point NT in new resolution to scale the image according to the original pixel values P1-PK and corresponding weights W1-WK corresponding to original pixel points N1-NK that form the target pixel point NT. Using the scaling system 200 of the invention, scaling between different image resolutions can be achieved so as to further drive a display (not shown) to display the scaled image and complete the image processing.

An original resolution Q before image scaling and a new resolution P to be scaled are provided to the scaling system 200. Microcontroller 210 receives the original resolution Q and generates a look-up table which has a number of table fields, each having a related reference value.

FIG. 3 shows an embodiment of a look-up table T according to the invention. In this embodiment, it is assumed that original resolution Q is 500 and new resolution P is 300. Thus, reference value of each table field on the look-up table T is generated according to original resolution Q. The first table field C1 has a field order 1 and a reference value U1, 31. The second table field C2 has a field order 2 and a reference value U2, 63 and so on.

As shown in FIG. 3, in this embodiment, the bit number n of multiplier is 4, so that look-up table T is divided into 16 (2n) table fields C1C16 according to the bit number n in which each table field has a related reference value. It should be noted that the reference values within the table fields on the look-up table T are 16 positive integers arranged from smallest to largest according to original resolution Q. As an example, in this embodiment, original resolution Q is roughly divided into 16 equal parts and all reference values of the table fields are arranged from smallest to largest in which each reference value can be obtained by accumulating a specific value. For instance, as shown in FIG. 3, if the original resolution Q is 500, the reference value U9 of table field C9 is 281, so reference value U10 of table field C10 can be obtained by following formula:
U10=U9+Q/16=281+500/16≈313.

Moreover, reference value U16 of largest table field C16 is set to the maximum possible value, 500 (i.e. original resolution Q) and reference value U1 of the smallest table field C1 is set to the minimum possible value. These reference values are used as a range when checking the look-up table T.

FIG. 4 is a flowchart of an image processing method according to an embodiment of the invention, used to generate a pixel value PT of a target pixel point NT according to one or more pixel values of original pixel points N1-NK. When applied in all original pixel points, the image can be scaled up or down. In this embodiment, it is assumed that the bit number n of multiplier is 4. First, in step S410, a set of original pixel points N1-NK and theoretical combination ratios R1-RK corresponding to original pixel points N1-NK to form the new pixel point NT are found. In this embodiment, the linear interpolation is used to obtain the set of original pixel points and the corresponding theoretical combination ratios R1-RK for scaling operation. The theoretical combination ratios depend on original resolution and target resolution. As shown in formulae (1)-(3), all of the theoretical combination ratios R1-RK can be obtained in advance using simple calculation and derivation, and thus the details are omitted here for brevity. Accordingly, in step S420, theoretical combination ratios R1-RK are converted to corresponding weights W1-WK ranging between 1 and 2n by checking a look-up table T or by operating. As shown in FIG. 3, look-up table T has been divided into 16 table fields in which each has a related reference value according to original resolution Q. Each theoretical combination ratio RK corresponding to the original pixel point NK is compared to the reference values to obtain an integer between 1 and 2n corresponding to the theoretical combination ratio RK by finding a reference value within a table field corresponding most closely thereto. The field order of the table field corresponding most closely to the reference value is set to the weight WK for the theoretical combination ratio RK.

For example, as shown in FIG. 3, if the theoretical combination ratio RK to be compared is 300, since reference value U9 of table field C9 is 281 and reference value U10 of table field C10 is 313, and 300 is between 281 and 313, the closest reference value for theoretical combination ratio RK (300) is 313 (reference value U10 of table field C10); therefore the weight WK corresponding to the theoretical combination ratio RK is set to the field order of table field C10, 10. Thus, according to the invention, a larger theoretical combination ratio 300 is converted to a smaller value 10. In step S430, each of the pixel values P1-PK of the original pixel points P1-PK in the set and corresponding weights W1-WK obtained from step S420 are calculated to generate pixel value PT of the target pixel point NT.

It should be noted that, in this embodiment, reference values within the table fields are arranged from smallest to largest, thus comparing and finding a reference value closest to the theoretical combination ratio RK entails finding the smallest reference value that exceeds or equals the theoretical combination ratio RK and field order of the table field related to the smallest reference value is the weight WK corresponding to the theoretical combination ratio RK. Nevertheless, the comparison for theoretical combination ratios R1-RK to find the corresponding weights W1-WK therefore may be obtained by other manners in some embodiments, such as by half-adjust rounding or rounding off method. For example, the corresponding weight WK is determined to be the field order of a first table field or the field order of a second table field using a half-adjust rounding or a rounding off method when the theoretical combination ratio RK is between a first reference value within the first table field and a second reference value within the second first table field.

In addition, if a target pixel value PT of a target pixel point NT in target resolution is theoretically composed of original pixel values P1-PK of original pixel points N1-NK in original resolution and k is an integer larger than 1, the corresponding weight WK can be obtained, without checking the look-up table, by the following in order to hold the sum of the corresponding weights W1-WK to be 2n:

W K = 2 n - i = 1 K - 1 W i
where the Wi represents the corresponding weights W1-WK-1 obtained by checking the look-up table.

For example, FIG. 5 shows an image in an original resolution Q which has 500 points scaled down to a new resolution P which has 300 points. In this example, bit number n of multiplier is 4 and linear interpolation is used for scaling operations. As shown in formula (1), a pixel value PA′ of a target pixel point NA′ is theoretically composed of original pixel values PA and PB of original pixel points NA and NB with theoretical combination ratios 300 and 200 respectively. In other words, the pixel set for target pixel point NA′ is (NA,NB) and the theoretical combination ratios RA and RB corresponding to the original pixel points NA and NB are 300 and 200 respectively. The same look-up table T having 16 table fields as described in FIG. 3 is generated according to original resolution Q. Accordingly, the look-up table T is checked to find a corresponding weight WA for theoretical combination ratio RA. Since the theoretical combination ratio RA is between reference value U9 and U10, it is obtained that the corresponding weight WA is 10 due to the field order for the reference value U10 is 10. Thus, the weight WB corresponding to the theoretical combination ratio RB can be derived by:
W B=16−W A=16−10=6
Formula (1) can be represented by formula (4) as:

P A = 10 P A + 6 P B 16 ( 4 )

As shown in formula (4), pixel value PA′ of pixel point NA′ can be determined using a 4 bit multiplier (i.e. bit number of multiplier is 4) and the division by 16 can be replaced by shifting right the result of (10PA+6PB) by four bits. Therefore, the pixel value PA′ of pixel point NA′ can be obtained without having a divider in the hardware.

Similarly, the pixel value PB′ of pixel point NB′ can be determined according to the remaining part of pixel value PB (i.e. 100) of original pixel point NB and pixel value PC of original pixel point NC. Formula (2) shows that:

P B = 100 P B + 300 P C + 100 P D 500 . ( 2 )

By checking the look-up table T, since 100 is between U3 (94) and U4 (125), the weight WB corresponding to the pixel point NB is found to be 4. In the same way, the weight WC corresponding to the pixel point NC is found to be 10 which is the same as weight WA. Therefore, the weight WD corresponding to the pixel point ND can be determined by following formula:
W D=16−W B −W C=16−4−10=2

Formula (2) can be represented by formula (5) as:

P B = 4 P B + 10 P C + 2 P D 16 , ( 5 )
where PD is the pixel value of pixel point ND. As shown in formula (5), pixel value PB′ of pixel point NB′ can also be determined using a 4 bit multiplier as previously discussed. Using the previously discussed operation, the formula (3) can be represented by formula (6) as:

P C = 7 P D + 9 P E 16 ( 6 )

Again, pixel value PC′ of pixel point NC′ can also be determined using a 4 bit multiplier as previously discussed. It should be noted that when a target pixel value PT of a target pixel point NT is theoretically composed of pixel values P1-PK of original pixel points N1-NK, the operations will be simplified by ignoring theoretical combination ratios less than a predetermined value. The theoretical combination ratio RK corresponding to a pixel point NK indicates a ratio for pixel value PK of the pixel point NK to form the target pixel value PT of the target pixel point NT, so the theoretical combination ratio RK can be ignored or its related weight set to zero if the theoretical combination ratio RK is less than a predetermined value. In this case, the pixel point next to the pixel point NK related to the ignored theoretical combination ratio RK is used to find the corresponding weight WK by checking the look-up table for simplification of the operations. According to the scaling method of the invention, a theoretical combination ratio RK corresponding to an original pixel point NK is first compared to a predetermined value before it is checked in the look-up table. When the theoretical combination ratio RK is less than the predetermined value, the theoretical combination ratio RK can be ignored or its related weight WK set to zero. This theoretical combination ratio RK can be added into theoretical combination ratio corresponding to the original pixel point next to the original pixel point NK for checking in the table.

For example, it is assumed that the predetermined value is 16 and the pixel value PD′ of target pixel point ND′ can be determined by:

P D = 10 P B + 300 P C + 190 P D 500 ( 7 )

In this example, when checking the table, the theoretical combination ratio corresponding to the pixel point NB is only 10 which is less than the predetermined value 16. Thus, the theoretical combination ratio 10 for pixel point NB is ignored and added into the theoretical combination ratio corresponding to next pixel point NC (300) so that the new theoretical combination ratio corresponding to pixel point NC becomes 310. Then, this theoretical combination ratio 310 corresponding to pixel point NC is used to check the table. By doing so, the formula (7) can be represented as:

P D = 10 P C + 6 P D 16 . ( 8 )

In sum, if a pixel value PT of a target pixel point NT in a target resolution P is theoretically composed of original pixel values P1-PK of original pixel points N1-NK in an original resolution Q with related theoretical combination ratios R1-RK respectively, the pixel value PT of the target pixel point NT can be obtained from:

P T = i = 1 K P i R i Q , ( 9 )
Where Ri is an integer between 1 and P. Using the method of the invention, the formula (9) can be converted to:

P T = i = 1 K P i W i 2 n , ( 10 )
wherein each of the corresponding weights W1-WK is an integer between 1 and 2n and the sum of the corresponding weights W1-WK is 2n.

The invention provides a method using only n bit of multiplier to reduce the bit number of multiplier and remove the divider for operation such that hardware cost and complexity are significantly reduced. In addition, the value of bit number n can be adjusted properly to gain a better performance for the related operations. These benefits will be better observed especially when the image to be scaled is a two- or more dimensional image.

FIG. 6A shows a relationship between original pixel points in an original resolution Q which has 500500 points and new pixel points in a new resolution P which has 300300 points when an image is scaled down from the original resolution Q to the new resolution P. As shown in FIG. 6A, the real line and dotted line area respectively represent the relationship for each pixel point in a 500500 resolution and in a 300300 resolution. In this example, a new pixel value PA′ of pixel point NA′ is formed by pixel values PA, PB, PC and PD of original pixel points NA, NB, NC and ND respectively. If a conventional bi-linear interpolation for 2-D (two dimensions) is used, the pixel value PA′ of new pixel point NA′ can be determined by:

P A = ( P A 300 300 + P B 200 300 + P C 300 200 + P D 200 200 ) 500 500 ( 11 )

The operations in formula (11), require at least two 9 bits of multipliers/dividers in the hardware. Moreover, these operations are time consuming.

FIG. 6B shows an image processing method according to an embodiment of the invention, showing a relationship between original pixel points in an original resolution Q which has 500500 points and new pixel points in a new resolution P which has 300300 points when an image is scaled down from the original resolution Q to the new resolution P. As shown in FIG. 6B, the real line and dotted line area respectively represent the relationship for each pixel point in a 500500 resolution and in a 300300 resolution.

In this example, if a 4 bit of multiplier is used, the factor for operation is to be 2n, that is, 16. For a two-dimensional image, each pixel point has horizontal and vertical coordinates. Therefore, a weight corresponding to such pixel point comprises a horizontal weight related to the horizontal coordinate and a vertical weight related to the vertical coordinate. To find the weights corresponding to theoretical combination ratios corresponding to the pixel points in a two-dimensional image, one look-up table for the horizontal coordinate and one look-up table for vertical coordinate are utilized, from which the corresponding weights can be found. For example, the weight WA corresponding to the theoretical combination ratio RA corresponding to pixel point NA can be represented as IXIY using the look-up tables, wherein IX represents the horizontal weight and IY represents the vertical weight corresponding to the theoretical combination ratio RA and both are integers between 1 and 2n. Once the weight WA is determined, the weight WB, WC and WD corresponding to the theoretical combination ratios RB, RC and RD corresponding to pixel points NB, NC and ND can also be determined by the following:
W B=(16−I X)I Y ,W C=(16−I X)I Y ,W D =I X(16−I Y),

Thus, formula (11) can be represented as:

P A = ( P A I X I Y + P B ( 16 - I X ) I Y + P C I X ( 16 - I Y ) + P D ( 16 - I X ) ( 16 - I Y ) 16 16 ,

From formula (11), original 300300 operations by 9 bit of multiplier are simplified using IXIY operations by 4 bit of multiplier and the operation for divided by 500500 also replaced by a operation for shifting the result generated by multiplier right by 8 bit, reducing not only the amount but the time needed for operations.

Although in the embodiment according to the invention the image is downscaled, it is to be understood that the invention can also be used for up-scaling in other embodiments. FIG. 7A shows an embodiment of a look-up table T for up-scaling an image according to the invention. FIG. 7B shows a conventional image up-scaling method for scaling original pixel points NA-NC within an image in an original resolution 300 up to pixel points NA′-NE′ in another resolution 500. Pixel values PA′-PE′ of the pixel points NA′-NE′ can be obtained by a conventional bi-linear interpolation using the following:

P A = 300 P A 300 , ( 1 ) P B = 200 P A + 100 P B 300 , ( 2 ) P C = 300 P B 300 , ( 3 ) P D = 100 P B + 200 P C 300 , ( 4 ) P E = 300 P C 300 , ( 5 )

For example, if pixel value PB′ of the original pixel point NB′ is to be obtained and theoretical combination ratio RA′ corresponding to the original pixel point NA is 200 which is known from formula (2)′, the weight corresponding to the theoretical combination ratio RA′ is set to 11 by checking the look-up table T (FIG. 3). Therefore, formula (2)′ can be represented as:

P B = 11 P A + ( 16 - 11 ) P B 16 , ( 2 ) .

Similarly, by converting the theoretical combination ratios corresponding to the pixel values PA′, PC′, PD′ and PE′ to integers between 1 and 16 using aforementioned method and rules, pixel values PA′, PC′, PD′ and PE′ of pixel points NA′, NC′, ND′ and NE′ can also be obtained as shown in FIG. 7C. Thus, the method according to the invention reduces not only the amount but the time needed for performing related operations when it is used to scale up an image.

While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to the skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

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Classifications
U.S. Classification382/299, 382/298, 345/3.4, 345/3.3
International ClassificationG06K9/32, G09G5/00
Cooperative ClassificationG06T3/4007
European ClassificationG06T3/40B
Legal Events
DateCodeEventDescription
May 15, 2014FPAYFee payment
Year of fee payment: 4
Jan 12, 2007ASAssignment
Owner name: PRINCETON TECHNOLOGY CORPORATION, TAIWAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:CHIA, HUI-FEN;TANG, YING-YUAN;REEL/FRAME:018793/0674
Effective date: 20061201